Generally, the nailing machine is so constructed that an actuating trigger valve can be operated by two operations, firstly, pulling a trigger lever which is provided so as to actuate the machine, and secondly, pushing a contact arm which is provided so as to slide along a nose portion for injecting a nail into a member to be nailed, thereby to actuate a striking mechanism.
Although the contact arm constitutes a safety device of the nailing machine in this manner, there has been known a type of the nailing machine in which a contact nose is coupled to a distal end of the contact arm, instead of using the contact arm as a single body, and a nail is driven from an injection port inside the contact nose. Because the contact nose is so constructed as to be integrally coupled to the contact arm, it is possible to dismount the contact nose from the nose portion by removing it from the distal end of the contact arm, and it becomes possible to use a plurality of the contact noses which are different in a shape of a distal end and an inside diameter of the injection port thereof, by exchanging them. Accordingly, it becomes possible to use the nails having different head diameters in a single nailing machine, by selectively mounting a plurality of the contact noses formed with the injection ports whose inside diameters are different from each other according to a head diameter of the nail to be used in the nailing machine (Reference should be made to JP-A-2005-161496).
However, because the inside diameter of the nose portion is formed so as to fit to the head diameter of a large nail among the nails to be used, the inside diameter of the contact nose too must be inevitably large. For this reason, in case where a small nail having a smaller diameter than a standard head diameter is used, this small nail is seriously inclined inside the injection port of the contact nose, and cannot be maintained in a favorable posture. Therefore, there is such anxiety that this small nail may be collapsed when it is struck. In fact, it has been difficult to drive the nail which is smaller than the standard nail, although it has been possible to drive the nail having the large head diameter and the nail having the standard head diameter.
Moreover, since a diameter of a driver is larger than the head diameter of the standard nail, a driving trace of the driver is formed on a surface of the member to be nailed, when this nail is driven into the member, and favorable finishing performance is unable to be secured.